1. Field of the Invention
The present invention relates, in general, to novel photoresist compositions useful for fabrication of semiconductor device and, more particularly, to an improvement in thermal resistance, resolution and sensitivity as well as light absorption at a band of i-line (wavelength 365 nm), along with the novel photoresist compositions.
2. Description of the Prior Art
As high integration of semiconductor device has been accelerated in the last few years, fine image-forming technologies useful for fabrication of semiconductor device become highly precise. Correspondingly, photoresist used in the fine image-forming technologies is required to have a combination of high sensitivity, high resolution, and superior thermal resistance.
As a fine image-forming technology, there is extensively employed a lithography technology which takes advantage of a g-line with a wavelength of 436 nm and an i-line with a wavelength of 365 nm from a mercury lamp, a light source. In addition, there are various methods, what is called, next generation lithography technology, using an excimer laser(KrF, wavelength 248 nm), an X-ray and an electron beam.
Phenol novolak/naphthoquinone diazide-benzophenone resist compositions are widely used for photoresist for UV (g-line, i-line). In these resist compositions, the benzophenone compounds serve as ballast and are exemplified by dihydroxy benzophenone, trihydroxy benzophenone, tetrahydroxy benzophenone and so on, as introduced in many patents, for example, U.S. Pat. Nos. 3,666,473, 4,115,128, 4,409,314 and 4,439,516, and Japanese Patent Laid-Open Publication Nos. Sho. 61-45240, Sho. 61-118744 and Sho. 62-280737. Herein, ballast means a kind of a latent compound which can function as a photosensitive agent through ether reaction of its photosensitive group, that is to say, a precursor compound having a photosensitive group.
However, since these exemplified compounds absorb light at a band of i-line which is most extensively used at present, the resulting photoresists are poor in transparency, which, in turn, deleteriously affects profile or resoultion. In addition, the exemplified benzophenone compounds have low solubilities in resist solutions.
It is generally required that a photosensitive agent used in photoresist be of high resolution, high sensitivity, superior thermal resistance, good pattern characteristic as well as superior compatibility with matrix resin. In last few years, various efforts have been made to synthesize such photosensitive agents as the above characteristics. For example, a research proceeded for a resist compound employing a polyhydroxy compound as a ballast (European Patent Laid-Open No. 0 440 238 A.sub.2).